A TIR-NLR gene from Arabidopsis Pla-1 confers resistance to geminivirus infection.

Geminiviruses are single-stranded DNA viruses that infect many plant species and cause serious losses in agronomically important crops. An earlier study showed that the Arabidopsis thaliana ecotype Pla-1 is resistant to infection by diverse geminivirus species and mapped the major resistance locus Geminivirus Resistance of Pla-1 1 (GRP1) to chromosome 1. In this study, we fine-mapped the GRP1 locus to a 0.6-Mb region and showed that its strength is gene-dosage-dependent. We also uncovered two minor resistance loci, GRP2 and GRP3, that mapped to chromosomes 3 and 5, respectively, and showed that GRP3 resistance is dependent on GRP1. RNA-Seq analysis of plants inoculated with the geminivirus, cabbage leaf curl virus (CaLCuV, Begomovirus brassicae), showed that AT1G31540, which is located in the GRP1 region and encodes a Toll/interleukin-1 receptor (TIR) type nucleotide-binding leucine-rich repeat receptor (NLR), is upregulated in Pla-1 compared to the susceptible Col-0. AT1G31540 specifies two TIR-NLR isoforms that contain non-synonymous codon differences between the two Arabidopsis ecotypes. Expression of the longer Pla-1 isoform, which includes a dual-segment leucine-rich repeat domain and an integrated domain at the C terminus, conferred CaLCuV resistance to Col-0, resulting in reduced viral DNA accumulation and no leaf chlorosis. In contrast, expression of the shorter isoform, which lacks the second leucine-rich repeat segment and the integrated domain, did not confer resistance. This study established that effector-triggered, TIR-NLR-mediated plant innate immunity contributes to geminivirus defense responses and identified a new host genetic resource to combat these important plant viral pathogens.